1. Field
The present invention is related to phased-array antennas and, more particularly, to low-cost active-array antennas for use with high-frequency communication systems.
2. Related Art
Phased array antennas (“PAA”) are installed on various mobile platforms (such as, for example, aircraft and land and sea vehicles) and provide these platforms with the ability to transmit and receive information via line-of-sight or beyond line-of-sight communications.
A PAA, also known as a phased antenna array, is a type of antenna that includes a plurality of sub-antennas (generally known as antenna elements, array elements, or radiating elements of the combined antenna) in which the relative amplitudes and phases of the respective signals feeding the array elements may be varied in a way that the effect on the total radiation pattern of the PAA is reinforced in desired directions and suppressed in undesired directions. In other words, a beam may be generated that may be pointed in or steered into different directions. Beam pointing in a transmit or receive PAA is achieved by controlling the amplitude and phase of the transmitted or received signal from each antenna element in the PAA.
The individual radiated signals are combined to form the constructive and destructive interference patterns produced by the PAA that result in one or more antenna beams. The PAA may then be used to point the beam, or beams, rapidly in azimuth and elevation.
Unfortunately, PAA systems are usually large and complex depending on the intended use of the PAA systems. Additionally, because of the complexity and power handling of known transmit and receive (“T/R”) modules, many times PAA systems are designed with separate transmit modules and receive modules with corresponding separate PAA apertures. This further adds to the problems relating to cost and size of the PAA system. As such, for some applications, the amount of room for the different components of the PAA system may be limited and these designs may be too large to fit within the space that may be allocated for the PAA system.
In addition to producing one or more antenna beams, the PAA also produces these one or more antenna beams with a predetermined polarization that is determined by the design of the PAA. The polarization of the PAA is intrinsic and is a property of the radiated signals that are the radiated waves produced by the PAA. These radiated waves propagate with a given orientation where the polarization of the PAA refers to the orientation of the electric field (i.e., the E-plane) of the radiated waves projected onto an imaginary plane perpendicular to the direction of motion of the radiated waves. In general, the radiated wave has elliptical polarization. A subset of this commonly used in communication antennas is circular polarization. This circular polarization may be “right-hand” circular polarization (“RHCP”) or “left-hand” circular polarization (“LHCP”), where a PAA that transmits and/or receives RHCP signals cannot receive LHCP signals and, likewise, a PAA that transmits and/or receives LHCP signals cannot receive RHCP signals because both these situations describe cross-polarized signals situations. The terms left-hand and right-hand are designated based on utilizing the “thumb in the direction of the propagation” rule that is well known to those of ordinary skill in the art.
In order to operate with both RHCP and LHCP, many PAA systems are designed as polarization switchable PAA systems that may switch operation from RHCP to LHCP and wise-versa. A problem with these polarization switchable PAA systems is that they are typically complex and expensive and not well suited for more cost conscious uses. As such, at present, there are many situations where non-switchable PAA systems with fixed circular polarization (either RHCP or LHCP) are designed and used. Unfortunately, once a PAA system is designed with a fixed circular polarization, it is very difficult and costly to redesign that particular PAA system design to operate with the opposite fixed circular polarization because typically the change in the polarization design of the PAA system will require a redesign, requalification, and remanufacturing of the integrated circuit chipset, which will have a significant impact on the cost and production schedule of producing the new PAA system. This is a problem if the particular PAA system has been designed for a particular custom use and/or for a particular vehicle where a change of polarization is desired (either for a new mission, use, or upgrade) and other useable PAA system designs are not readily available.
Therefore, there is a need for an apparatus that overcomes the problems described above.